The present invention relates to monitoring equipment for geomembranes and, in particular, to a system for monitoring leaks at elastomer swimming pool liners.
Pin hole leaks at large liquid impoundment membranes, such as a swimming pool liner, can result in large volumes of lost water. For example, leaks may occur from defects in the material, punctures or cracks that develop with age or exposure to ultraviolet light or normal use. In contrast to broken plumbing fittings or conduits, the leaks can occur anywhere in the surface of the membrane and are extremely difficult to locate. That is, the leak size is not typically susceptible to visual observation. Water clarity, light diffraction, and patterns formed in the liner also frequently hinder direct viewing for leaks.
For a swimming pool, depending upon the numbers and the locations of the leaks and the pressure of the liquid, the loss of liquid can be large, for example, on the order of 500 to 1000 m gallons per day or more. Additional liquid must be frequently added to compensate for the losses and the chemicals must be re-balanced. Over time, the operating costs to maintain the pool can increase. For impoundments of hazardous liquids, groundwater affecting leakages can be especially costly.
A variety of methods and equipment have been developed to address comparable problems for a variety of applications. U.S. Pat. No. 4,309,576 discloses a portable acoustic detection system for use with an impounded liquid. U.S. Pat. No. 4,905,210 discloses the use of a hydrophone array. U.S. Pat. No. 4,357,113 discloses a system which uses an array of thermal sensors.
Various systems which induce DC voltage gradients into the impoundment are also known. U.S. Pat. No. 4,720,669 monitors the changing current density at a hemispherical probe and a portion of the liquid trapped beneath the probe. U.S. Pat. No. 4,751,467 measures current changes through a skirt and a second liquid contained between the skirt and impoundment membrane. U.S. Pat. No. 4,740,757 measures magnetic field changes through a second liner and a contained liquid between the first and second liners. U.S. Pat. Nos. 4,719,407 and 4,725,785 measure changing voltage gradients in the impounded liquid with an RF controlled probe and a radially rotated probe. PCT application WO 87/03987 discloses a system which measures gradient changes with a portable differential probe.
U.S. Pat. No. 4,565,965 provides a pulse amplitude measurement system for monitoring leaking roof liners.
In contrast to known systems, the present invention provides a portable monitoring system having a directionally sensitive probe. A low frequency AC (e.g. 5-15 Hz full square wave) signal is impressed into the liquid and a portable, pole mounted probe monitors current gradients established in the liquid to provide a highly accurate indication of a leak location.